What is a more useful business language to learn Chinese or Japanese?

Of course, Chinese. China's increasingly powerful stature and more business opportunities relating to the Chinese language means it has become one of the world's most important business tools. It is critical to the success of business negotiations.

But on the other hand, this is based on the assumption that China's stature is indeed increasingly powerful and will continue to increase in the longer term. Consumption wise, the average Chinese-speaking person has yet to reach the level of the average Japanese-speaker.

So if it is possible, learn both languages if you are interested in engaging Northeast Asia. To the native English-speaker, Japanese could be the more difficult language to learn, but it all depends on other factors like whether you have the benefit of good teachers who are able to explain in English when it is needed, and/or whether you have Japanese-speaking friends who are more than willing to converse in Japanese with you.

Also, by learning Chinese characters you basically acquired part of the Japanese language; and by learning the Japanese Kanji characters you acquired part of the Chinese language.